My first impression is that the Windows Boinc 5.5.16 works flawlessly behind NTLM. Each communication is done at the first try, no unsuccessful retries...

I tried to update Seti Beta, Boinc contacted the proxy, upon request immediately continued with authentication (no more attempts to go on unauthenticated), succeeded with it and sent request + received answer. (Then, off course, Pirates attempted few times to get a piece of work too and immediately got clear answer "Pirates@Home|Scheduler RPC succeeded [server version 503] - No work from project" within few seconds.

Some while later Malaria finished and then successfully uploaded its result in 4 seconds (exactly mixed with Pirates' request for work, which took 5 seconds). Then I manually reported Malaria's work, it took 5 seconds and said "malariacontrol.net beta|Scheduler RPC succeeded [server version 504]".

I hope the NTLM nightmare could be considered to be solved ;-)
But will keep it in eye...

If maybe Walt would be interested in my logs, I've switched on following flags (among others, while playing with them, ncpus=2 is a nice toy :) - file_xfer file_xfer_debug http_debug proxy_debug net_xfer_debug. Now I'm listening also to the boinc_alpha stream (but still too shy to post there :)

My first impression is that the Windows Boinc 5.5.16 works flawlessly behind NTLM. Each communication is done at the first try, no unsuccessful retries...

My second impression is the same. Tried with 3 different projects - upload and report, first without authentification (I forgot to switch it on) - correctly failed, then authentificated - it correctly went through.

Not happy to break your optimism...
Still cannot connect, even in 5.6.0.
I can try to set messages more detailed (actually I already did it), but there are some details obout our company proxy, which I don't want to spread over i-net. I can send detailed message list to Rom Walton or other BOINC team member, if the want it.

I had no time last month in work, so first testing today. Last week I just updated to BOINC 5.6.4, but no progress on my side. When I press <Retry> in Upload/Download tab, file status change to "Uploading" size goes up from i.e. 0/9.99 KB to 10.71/9.99 KB and then it stays for five minutes. After five minutes http error is announced.
The same behaviour is in BOINC 5.6.5

I have to wait for five minutes now and then I will messages to you, Ageless.